I lived in MyYami for many years, and generally dove north or south of the city unless I was on a private boat. The dive ops in there are typically pretty shoddy. Lots of slick people being cool, cell phones ringing during surface intervals, no-information briefings (if they bother to give a briefing), etc. Leave on time? (maybe, probably not) Head to the site you booked on the phone? (usually not because the DM or capt is trying to hustle one of the bikinied tourist customers rather than attending to the diving.)
I once booked a trip out of Key Biscayne and never did find out who the DM was, or what sites we dove. How did I know who the capt was? I'm assumming it was the cat who was at the capt station the longest (one guy stayed there about 50% of the time; two others split the remainder of the time. There was no briefing)
Too bad the dive ops are so poor quality, because there is some fantastic diving there. But if you head to Homestead and dive the national park, or on down to the Keys, or drive up to Ft Lauderdale area or Boca/Delray/Boynton, you'll find the dive ops AND the diving to be delightful. And its all within an hour of glitterville.
Now for sightseeing & people watching, you can't do better than South Beach!